During such interventions, a surgeon holds the tool with the hand, for example, and moves the tool relative to the tissue to be treated in order to perform manipulations on the tissue. These movements and manipulations are performed under visual supervision. For assisting the visual supervision, the surgery systems provide a microscope, for example. The microscope generates an image of the tissue to be treated and the tool in a top view. It is difficult for the surgeon to estimate the distance from the tool to the tissue. Sensitive tissue may be damaged when unintentionally touched and/or pressure is applied to the tissue by the tool. An example for such an intervention are surgeries on the retina of an eye which are performed with help of a surgery microscope having an integrated OCT system. The OCT system allows to generate cross-sectional images of the tissue layers of the retina and to identify regions to be treated within these images. In this case, the movements with the tool necessary for the treatment are performed by the surgeon under visual supervision using the surgery microscope by viewing into the oculars of the surgery microscope.
It has already been proposed to perform an approach of the surgical tool to the tissue to be treated not only under the visual supervision, which is possible by means of the microscope image, but also by accounting for the images generated by the OCT system. However, this is problematic as tools are badly visible in OCT images and tissue regions disposed in the beam path of the OCT system behind the tool are shadowed so that it is also difficult to estimate the distance between the tool and the tissue layers from the OCT images. Furthermore, OCT scans of large object areas, where the tool may be located eventually, require relatively much time so that representations of the tool and the tissue regions cannot be obtained from OCT scans in real-time in a satisfactory manner.